During the production of a hydrocarbon well, it is necessary to monitor the relative volumetric flow rates of the different phases (e.g. oil, gas and water) of the multiphase fluid mixture flowing into the pipe of the well from the hydrocarbon bearing zones. Further, current hydrocarbon well often comprises vertical well section, deviated well sections and horizontal well sections. The interpretation of the flow in such complex wells is challenging because small changes in the well inclination and the flow regime influence the flow profile. Thus, an accurate monitoring requires sensors or probes capable of imaging a surface section or a volume section of the pipe and providing an estimation of the surface section or the volume section occupied by each phase.
Production logging of hydrocarbon wells (e.g. oil and gas wells) has numerous challenges related to the complexity of the multiphasic flow conditions and the severity of the downhole environment.
Gas, oil, water, mixtures flowing in wells, being either openhole or cased hole wells, will present bubbles, droplets, mist, segregated wavy, slugs structures depending on the relative proportions of phases, their velocities, densities, viscosities, as well as pipe dimensions and well deviations. In order to achieve a good understanding of the individual phases flowrates and determine the relative contributions of each zones along the well, an accurate mapping of fluids types and velocities is required on the whole section of the hole (openhole well portion) or pipe (cased well portion) at different depth (i.e. the measured depth is different from the true vertical depth and generally longer than true vertical depth, due to intentional or unintentional curves in the well).
Further, production issues greatly vary depending on reservoir types and well characteristics resulting in the need for a flexible production logging technology working with different types of sensing physics. For example, due to the phases segregation, deviated wells showing high water cuts require an accurate detection of thin oil layer at the top of the pipe. The effect of well inclination will have a strong impact on velocities and holdups.
Furthermore, high pressure, up to 2000 bars, high temperature, up to 200° C., corrosive fluid (H2S, CO2) put constraints on sensors and tool mechanics.
Furthermore, solids presence in flowing streams can damage equipments. In particular, the sand entrained from reservoir rocks will erode parts facing the fluid flow. Solids precipitated from produced fluids due to pressure and temperature changes, such as asphaltenes, paraffins or scales create deposits contaminating sensors and/or blocking moving parts (e.g. spinners).
Furthermore, the tool deployment into the well can be difficult and risky. In highly deviated or horizontal wells, tools must be pushed along the pipe using coiled tubing or pulled using tractor which is difficult when tools are long and heavy. Pipes may be damaged by corrosion or rock stress which may create restrictions and other obstacles. During the logging operation, equipments can be submitted to high shocks. Thus, in such environments, it is highly preferable to have light and compact tools.
Furthermore, the cost is also an important parameter in order to provide an economically viable solution to well performance evaluation even in mature fields having low producing wells in process of depletion with critical water production problems.
With respect to the hereinbefore described challenges, the state of the art production logging equipments have limitations.
Certain production logging tools available on the market have limited or no pipe section imaging capabilities and work correctly only in near vertical wells. These tools use a gradiomanometer and/or capacitance sensor to identify fluid entries. Further, these tools use spinner rpm and insitu calibration data to compute holdups and flowrates.
Other production logging tools available on the market are intended to identify fluid types from local probe sensors (electrical or optical) and to compute the fluid velocities from miniaturized spinners. Some of these production logging tools comprise probes attached to the centralizer arms creating a two dimensional (2D) array of local measurements. Achieving sufficient coverage requires a large number of arms/probes which leads to complex and expensive designs, tool maintenance is complex and reliability is poor. In addition, the measurements on different phases are made at different positions on a long tool string resulting in interpretation issues. Another production logging tool comprises a one dimensional (1D) array of sensors attached to a moving arm providing a scan of measurements along one line of the pipe section. Thus, the measurements coverage is limited and, depending on tool position, some production zone may be missed. The operation of such complex and costly tools results in important deployment difficulties that render compulsory the presence of highly trained engineering teams on the field.
Other attempts have been made to develop tools with rotating arms in order to improve coverage. The documents U.S. Pat. Nos. 5,531,112 and 5,631,413 describe a production logging tool for use within a well to determine fluid holdup of a multiphase fluid flow within the well. The production logging tool includes a plurality of sensors secured within a plurality of arms which radially extend from a tool housing to points distal from the tool housing. A plurality of sensors are included within the plurality of arms for detecting variations in fluid properties attributable to different flow constituents of the multiphase fluid flow along a path which circumscribes an exterior of the tool housing. The plurality of arms are rotated about the tool housing for moving these sensors through the path in order to ensure that the volumetric proportions of the different flow constituents of the multiphase fluid flow are accurately detected in highly deviated and in horizontal wells. Such production logging tools are complex apparatuses. Their reliability is problematic when taking into account the harsh downhole environment of hydrocarbon wells. In particular, the difficulty of operating motor/shafts mechanics under high pressure and complexity of rotating electrical connections kept such development at prototype level and technology has never been commercialized.